1. Field of the Invention
The invention relates to the field of optical coherence tomography, and in particular to an improved optical system in which optical coherence tomography is performed.
2. Description of the Prior Art
Three-dimensional high resolution optical imaging has potential clinical applications in the emerging field of biomedical optics. In a conventional optical imaging system, axial and lateral resolutions are correlated. Hence, one cannot obtain both in the same system. Optical coherence tomography (OCT) is a new modality that provides high resolution sub-surface microstructural images in a noninvasive manner. OCT uses coherence gating to select minimum backscattered photons for image reconstruction. Axial and lateral resolutions are determined by the source coherence length and numerical aperture of the sampling lens, respectively. While axial resolution can be improved using a broadband light source, there is a trade-off between lateral resolution and focusing depth when conventional optical elements are used, e.g. spherical lenses, mirrors, etc., because a beam with a long focal depth and narrow lateral width cannot be produced simultaneously. While high lateral resolution imaging requires a large numerical aperture, a long focal depth requires a small numerical aperture. In high speed OCT imaging, where an axial scanning mode (A-mode) is used, a tightly-focused lens produces a micrometer sized spot at only one particular depth. The coherence gate quickly moves out of the shallow depth of focus during the scan. Although dynamic focusing compensation can be used to overcome this limitation, current lenses can only be used at low speeds, which limit their use to low frame rate OCT systems. In addition, dynamic focusing lenses are bulky and cannot be implemented in circumstances where physical space is limited such as endoscopic OCT.
What is needed is some means or methodology whereby these limitations of the prior art can be overcome without creating a disadvantage in some other aspect of operation.